Plastic closures and liners, and methods of producing these closures and liners are known in the art. These liners are typically used as liners for the closure of a reclosable glass or plastic container, especially glass or plastic bottles. The liners provide sealability and sealing integrity under top loading conditions, and easy reclosability. Sealing integrity can be defined as the force required to effectively seal a container while maintaining its internal pressure. Generally, a minimal amount of force is preferred. A satisfactory liner composition for both glass and plastic containers is characterized by the ability to be consistently formulated, and processed, e.g. by compression molding, using conventional apparatus and methods.
Closures are generally required to have a minimal threshold removal torques, carbonation retention, carbonation retention under top load and satisfactory functioning on a container when cycled through environmental changes of temperature and humidity.
Most closures and closure liners in commerce are produced singularly or in combination from a plasticized polyvinyl chloride (PVC), polyethylene, EVA copolymer and an oil-extended thermoplastic elastomer.
Blends that have the following properties are suitable to be used as linear material and for the manufacture of closures:
______________________________________ Compression Set: &lt;70% Hardness, Shore A: &lt;85 Tensile Yield Strength: 1,000 to 2,000 psi ______________________________________
These polymer materials and the closures and liners made from the previously enumerated polymers have the following non-exclusive problems or drawbacks.
Polyethylene is not soft and elastic enough to sustain the internal pressure that is generated inside the bottle or container by the carbonated beverage, and it also does not have enough creep resistance to provide reclosability to the closure.
Liners or closures made from rubber or elastomeric blends contain a significant portion of a low molecular weight mineral oil. The oil in the liner formulation can be extracted by the contained beverage, and introduce foreign material into the beverage, and consequently impair the odor and taste of the beverage.
It is known in the art that plasticized PVC has high removal torque which causes inconvenience to users, especially elderly users and children. It is known that it is not-recyclable with other polyolefins such as polypropylene.
Liners or closures made from EVA copolymer when subjected to elevated temperature during the extrusion and/or compression stage, tends to decompose and give off acetic acid which causes organoleptic problems in food packaging. Even after the parts made with EVA are cooled and solidified, it impairs the taste and odor of the food or beverage that comes in contact with the plastic surface.
It is an unsolved problem of the art to provide polymer materials useful in the manufacture of closures, and as closure liners that do not have the drawbacks associated with liners known in the art.